The present invention relates to a method and apparatus for controlling the rotation of an optical disk, and more particularly, to a method and apparatus for controlling the rotation of an optical disk on which pre-grooves are formed for providing a wobble signal frequency-modulated by data for rotationally controlling the optical disk at a constant linear velocity.
In general, an optical disk, for example, a mini disk whose rotation is controlled at a constant linear velocity (the velocity of a track passing a laser beam during tracking), is provided at the time of manufacturing the disk with pre-grooves having address information. The pre-grooves are alternately formed on left and right address areas of the track's center, such that a wobbled form is created. The signal obtained from the wobbled pre-grooves is called a wobble signal. The wobble signal is a signal for frequency-modulating a 22.05 kHz subcarrier using the data having address information, and the frequency-modulated signal is 22.05kHz.+-.1 kHz. The aforementioned data is a data signal biphase-modulated after coding physical location information, for example, an absolute time information, on a disk and adding an error correction mark.
In a method for controlling the rotation of an optical disk provided with such pre-grooves, an optical beam is irradiated on the address area of the optical disk, and the light reflected therefrom is converted into a current signal to thereby ,obtain the wobble signal. Then, the phases of the reproduced wobble signal and a reference signal are compared to generate a rotation control signal which controls the rotation of the spindle motor for driving the rotation of the optical disk.
In U.S. Pat. No. 5,109,369, there is disclosed system which regulates the phase by a bit clock demodulated from a wobble signal to control the rotation of a disk. The phase control occurs at the time of a demodulation error. Also, the wobble signal period is counted by a speed counter so that a speed control signal combined with the phase control signal is generated.
However, in such a conventional rotation control system, when an operational abnormality occurs, i.e., when a demodulation error in the wobble signal is generated due to an external shock or a track jump, the wobble signal deviates from the phase control range and the control of the disk rotation becomes unstable. Also, when the rotational speed of a disk undergoes a rapid change (either too fast or too slow) due to the operational abnormality and, as the result thereof, the phase goes rapidly amiss momentarily, it is difficult to bring the disk rotation status under control immediately merely by phase-control using the wobble signal. This is because, for phase control, a phase difference between a reference signal and a compared signal is detected, and this slows the response time of the controlling operation.